In general, for high density recording such as digital recording or video recording, a recording and/or reproducing system (hereinafter referred to as a record-reproduce system) having a rotating head of a helical scan type is used.
For loading in a record-reproduce system of such a type, there has been proposed a tape cassette of a very small size (about 20 mm long and 30 mm wide in planar dimensions). Such a tape cassette includes a shell body having an opening for insertion and extraction of a head drum, and a ribbonlike recording medium which is windingly packed in the shell body and which is wound on the outside circumferential surface of the head drum.
Explanation is made about this tape cassete with reference to FIGS. 18.about.20. In these figures, what is indicated at a reference numeral 1 is a tape cassette shell body. This shell body 1 consists of upper and lower halves 3 and 4 fixed together by screws 2a.about.2d. The shell body 1 has a cassette opening 5 in a front side for insertion and extraction of a later-mentioned head drum.
Each half 3, 4 of the shell body 1 has vertically extending through holes 3a, 3b, 4a, 4b. Between both through holes 3a, 3b or 4a, 4b, a transparent plate 6, 7 for checking a residual amount of the tape is attached to cover a rectangular, as viewed in a plan view, opening 3c, 4c of each half.
In each half 3, 4 of the shell body 1, there are further formed mis-erase preventive setups 8, 9 located in both lateral portions near a rear side of the half and extending into the half, reference holes 10, 11, 12, located in the middle and left and right lateral portions near the rear of the half, for positioning the cassette, a plurality of check holes 13, 14 which are arranged at intervals along the left and right direction in the rear portion of the half, and grip portions 15, 16 located in both lateral rear portions.
In each lateral front end portion of each of the halves 3, 4, there is formed a stepped shaft supporting surface 20 having a laterally projecting pin 18, and stopper surface 22 continuous with the shaft supporting surface 20. (These features are formed on both the left and right lateral front end portions, although only the right portion is shown in FIG. 18.) In a stepped portion 20a of the shaft supporting surface 20, there is integrally formed a vertically extending click projection 23.
In the bottom of the lower half 4 among both halves 3, 4, there is formed a recessed portion 25 opening toward the upper half, for receiving a brake. In this recessed portion 25, there are provided brake spring abutting projection 26, and brake guide pins 27, 28 arranged at intervals in the front and rear direction.
Reference numerals 29 and 30 denote tape winding hubs spaced at a predetermined distance from each other. Each hub consists of an inner hub 31, 32 having a through hole 31a, 32a for receiving a hub driving shaft, and a projected portion (not shown) for controlling the rotation, and an outer hub 33, 34 surrounding the inner hub and having a recessed portion (not shown) engaged with the above mentioned projected portion. The hubs are located in the positions corresponding to the holes 3a, 4a, 3b, 4b of each half 3, 4, and rotatably supported within the shell body 1. The inner hub 31, 32 of each hub 29, 30 is provided with a plurality of hub engaging portions 31b, 32b projecting in the outside circumferential surface and being exposed in the shell body. A magnetic tape T serving as a ribbonlike recording medium for recording and/or reproducing PCM signals, for example is wound on the outside circumferential surfaces of the outer hubs 33, 34.
A reference numeral 35 denotes a brake for braking the hubs 29, 30 when the cassette is out of use. The brake 35 includes an approximately T-shaped, in a plan view, brake piece 36 having arms 36a, 36b projecting toward both lateral front ends, and spring engaging portions 36c, 36d projecting forwardly of the arms 36a, 36b; and a brake spring 37 such as a stainless wire which is held by the engaging portions 36c, 36d of the brake piece 36 so as to abut on the projection 26, and which extends in the left and right direction. The brake 35 is provided in the recessed portion 25. The brake 35 has detents 38, 39 projecting rearwardly of the arms 36a, 36b and engaging with the engaging portions 31b, 32b during braking; guide portions 40, 41 for guiding the pins 27, 28; and a push operating portion 42 having cam surfaces 42a (only one of which is shown) on which a positioning pin (not shown) abuts when the cassette is loaded.
Reference numerals 43 and 44 denote pinch rollers for guiding the magnetic tape T. The pinch rollers are rotatably provided through roller shafts 45, 46 on both sides of the opening 5.
Reference numerals 47 and 48 denote vertically extending support pieces which are integrally provided with respect to the upper half 3 so that projecting end portions abut on the lower half 4.
Reference numerals 49 and 50 denote guide projections for preventing the tape from being forced out of the shell body 1. Each guide projection 49, 50 consists of upper and lower projections having projecting end surfaces confronting each other. These projections are located on the outer sides of the support pieces 47, 48, and each is integrally provided in the corresponding one of the upper and lower halves 3, 4.
Reference numerals 51 and 52 denote self aligning guides having grooves 51a, 52a for guiding the magnetic tape T. These guides 51 and 52 are movably provided through pivot shafts 53, 54 in the lower half 4.
A reference numeral 55 denotes a U-shaped lid for shutting the cassette opening 5. The lid has a cover portion 57 for opening and closing the cassette opening 5, and two arms 58, 59 projecting from both sides of the cover portion 57, and confronting the shaft supporting surfaces 20 contiguously. The lid is rotatably provided on the upper half 3 of the shell body 1. The cover portion 57 of the lid 55 is formed with a guide groove 57a extending in the left and right direction, and a rack gear 57b for engaging with a cassette changer (not shown). The arms 58, 59 are formed with shaft holes 58a, 59a for the pins 18, and click grooves 59b corresponding to the click projections 23.
A reference numeral 60 denotes a head drum having an outside peripheral surface on which the magnetic tape T is helically wound, and a reference numeral 61 denotes a head which rotates while being inclined at a predetermined angle with respect to the head drum 60. Reference numerals 62 and 63 denote wing guides which are provided on both sides of the head drum 60 and which are inserted into and extracted from the cassette opening 5. Reference numerals 64 and 65 denote flanges which are provided at the projecting ends of the wing guides 62 and 63 and which locate the magnetic tape T with respect to the head drum 60 in the widthwise direction.
In the thus-constructed tape cassette, the magnetic tape T is helically wound on the outside peripheral surface of the head drum 60 by insertion of the head drum 60 in the cassette opening 5 of the shell body 1, and then the head 61 runs obliquely with respect to the magnetic tape T, so that the helical scan type recording and/or reproducing operations are performed.
In this kind of tape cassette, on the occurrence of a positional shift of the tape cassette during insertion of the cassette in the record-playback equipment, or an error in the inclination of the head drum, the head drum 60 inserted in the opening 5 does not abut the self aligning guides 51, 52 in the correct state, and the sliding movement of the magnetic tape T on the outside surface of the head drum 60 becomes unstable, which incurs troubles in recording and/or reproducing.
Therefore, in the conventional tape cassette, the self aligning guides 51 and 52 are made rotatable around the pivot shafts 53, 54, and the tape guides are made inclinable with respect to the shafts 53, 54, and movable back and forth in the lateral direction perpendicular to the inserting and extracting direction of the head drum 60. With the thus-arranged tape guides movable relative to the shell body 1, the magnetic tape T is put in sliding contact with the outside surfaces of the self aligning guides 51, 52 in a stable state to perform the recording and/or reproducing. This is what the conventional cassette takes as countermeasures.
In the conventional tape cassette, however, the pinch rollers 43, 44 are not swingable, and the receiving portions of the pinch rollers 43, 44 are located at positions shifted downwardly from the middle in the axial direction. Furthermore, the roller shafts 45, 46 are arranged as a cantilever structure. Therefore, when the tension of the magnetic tape during recording and/or reproducing causes an excessive force acting in the radial direction of the roller, then this cassette cannot gain a sufficient self aligning effect for correcting the inclinations of the roller shafts 45, 46. As a result, there arises need for stringently controlling the dimensional accuracy and assembling accuracy of the component parts of the cassette in order to obtain the ideal tape path, so that the cassette manufacturing and assembly process is complicated
Besides, the cantilever supporting structure of the roller shafts 45, 46 makes it easy for the roller shafts 45, 46 to bend due to the pressure of a capstan, and the persistence of this bent state results in creep deformation.
In the conventional tape cassette, moreover, if the cassette is loaded in the record and reproduce equipment in such a state that the self aligning guides 51, 52 are juxtaposed in the up and down direction, the self aligning guide 51 on the upper side becomes unable to fitly approach the downwardly shifted head drum 60 under the circumstances in which the degree of freedom of motion of the self aligning guides 51, 52 in the up and down direction is lower than the degree of freedom of motion of the head drum 60 in the up and down direction. Therefore, the head drum 60 must move up and become fitted to the self aligning guide 51 on the upper side. It is conceivable that this occurs especially when there exist a positional error of the wing guide 62, 63 with respect to the head drum 60 in the drum inserting direction or in the approaching direction of the wing guides, a dimensional error between both self aligning guides 51, 52, and dimensional errors of both elongate guide holes (not shown) of the self aligning guides 51, 52.
Consequently, the resistance in movement of the head drum 60 increases, and there is formed, between the head drum 60 and the self aligning guide 51, a gap of a size corresponding to the weight of the head drum 60, the frictional force loss due to the pressure of the self aligning guide 51 and the elongate guide hole (not shown) or the frinctional force loss of the head drum 60 and a drum supporting portion (not shown) during movement of the drum in the front and rear direction. This gap deteriorates the recording and/or reproducing performance.